Food Bioprocess Technol DOI 10.1007/s11947-012-0877-7
ORIGINAL PAPER
Total Phenolics, Flavonoids, and Antioxidant Activity of Sage (Salvia officinalis L.) Plants as Affected by Different Drying Methods Ibtissem Hamrouni-Sellami & Fatma Zohra Rahali & Iness Bettaieb Rebey & Soumaya Bourgou & Ferid Limam & Brahim Marzouk
Received: 5 August 2011 / Accepted: 23 April 2012 # Springer Science+Business Media, LLC 2012
Abstract In the current study, we determined the effects of seven drying methods on total phenolics, flavonoids, individual phenolics, and antioxidant activity of the methanol extract of Salvia officinalis L. As compared with total phenolic content (TPC) of fresh plants, results showed that the highest TPC was recorded in plants dried by microwave (MW) at a power of 800 W/30 g of fresh plant and was 4.2 times higher than that of fresh plants whereas the lowest content was found in the case of plants dried by far-infrared (FIR) at 45 °C. The analysis of the different extracts by RPHPLC showed a predominance of phenolic acids particularly in fresh plants and those dried by MW (600 W/30 g of fresh plant) whereas flavonoids predominate in the case of plants dried by FIR (65 °C). The assessment of the radical scavenging activity (RSA) against the stable radical 1,1diphenyl-1-picrylhydrazyl (DPPH) showed an increase in the scavenging effect particularly in MW (800 W/30 g of fresh plant) dried plants with an IC50013.49 μg ml−1 (IC50 is the concentration required to cause 50 % DPPH inhibition). The complementary assessment of the RSA using the β-carotene/linoleic acid system showed an increase of this activity for all extracts and particularly for the extract derived from MW (600 W/30 g of fresh plant) dried plants as compared to fresh ones. Finally, all the plant extracts showed moderate reducing power as assessed by the ferric-reducing antioxidant potential. These results suggested that MW drying could be applied to retain phenolic
I. Hamrouni-Sellami (*) : F. Z. Rahali : I. B. Rebey : S. Bourgou : F. Limam : B. Marzouk Laboratory of Bioactive Substances, Center of Biotechnology of the Techno pole Borj-Cedria, BP. 901, 2050 Hammam-Lif, Tunisia e-mail:
[email protected]
contents and to enhance antioxidant activity of sage plant materials. Keywords Salvia officinalis L. . Drying . Microwave . Far-infrared . Phenolics . Flavonoids . Antioxidant activity
Introduction In recent years, plants extracts have appeared on the market as antioxidants for food industry use. The antioxidant capacity of some of these extracts has been proved to be comparable to and sometimes higher than that of synthetic antioxidants (Pokorny 1991). In particular, the Lamiaceae family includes a large number of plants that are wellknown for their antioxidant properties (Tosun et al. 2009). Among these, the aerial parts of common sage (Salvia officinalis L.) have been widely used to produce antioxidants and most of their antioxidant components have been identified (Tosun et al. 2009). Together with Rosmarinus officinalis L., S. officinalis L. have been shown to have the strongest antioxidant activity among herbs (Madsen et al. 1997). Some of their phenolic compounds have revealed excellent scavenging activity of active oxygens such as superoxide anion radicals, hydroxyl radicals, and singlet oxygen (Masaki et al. 1995), inhibiting lipid peroxidation (Hohmann et al. 1999) and consequently, the corresponding extracts have been widely used to stabilize fat and fatcontaining foods (Ternes and Schwarz 1995). The main effective antioxidant phenolic compounds have been shown to be phenolic acids, carnosol derivatives, and flavonoids, namely, rosmarinic acid, carnosic acid, and carnosol followed by caffeic acid, rosmanol, rosmadial, genkwanin, and cirsimaritin (Cuvelier et al. 1996).
Food Bioprocess Technol
Drying, as a preservation method, is a very important aspect of food processing. The main function of drying is to lower the water activity of the product and consequently, to inhibit the growth of microorganisms and decrease chemical reactions in order to prolong the shelf life of the product at room temperature. It also results in less space needed for storage and lighter weight for transportation. Drying can either be performed by traditional sun/shade drying or microwave drying/oven drying (Sathishkumar et al. 2009). However, enzymatic and non-enzymatic processes that may occur during drying fresh plant tissues may lead to significant changes in the composition of phytochemicals (Capecka et al. 2005). Generally, these processes may cause negative consequences to the final food product. Studies by Nicoli et al. (1999), however, proved that the overall antioxidant properties of certain foods may instead be enhanced due to the formation of Maillard reaction products (MRPs), which results from a condensation reaction between amino acids (or proteins) and reducing sugars or lipid oxidation products. These MRPs exhibited antioxidant activity as measured by 1,1-diphenyl-2-picrylhydrazyl and β-carotene bleaching assays. However, the reducing power and iron chelating abilities of MRPs were also reported to increase upon irradiation to scavenge hydroxyl and superoxide anion radicals under in vitro conditions (Chawla et al. 2009). Finally, some recent studies have shown that drying some plant materials could enhance their polyphenolic contents. For example, an increase in polyphenolic content after drying has been reported for tomatoes (Chang et al. 2006) and shiitake mushroom (Choi et al. 2006). Drying has also been reported to affect the antioxidant activity of fruits and vegetables diversely (Choi et al. 2006; Park et al. 2006; Chantaro et al. 2008; Kuljarachanan et al. 2009). In recent years, microwave (MW) drying has gained popularity as an alternative drying method for a variety of food products such as fruits, vegetables, snack foods, and dairy products (Wang and Sheng 2006). In fact, air drying is one of the more energy-consuming processes, and thereby, industries using energy-intensive processes are being forced to explore ways for reducing their energy consumption (Ould Ahmedou et al. 2008). The principle of drying using microwave energy is based on the direct effect of the microwaves on molecules by ionic conduction and dipole rotation. Polar molecules absorb strongly microwave energy because they have a permanent dipole moment, which results in rapid temperature rise and in fast completion of drying (Eskilsson and Bjorklund 2000). On the other hand, the use of far infrared (FIR) radiation technology in dehydrating foods has several advantages. These may include decreased drying time, high energy efficiency, high-quality finished products, uniform temperature in the product while drying, and a reduced necessity for air flow across the product (Mongpreneet et al. 2002). Far infrared radiation was
thought to liberate and activate low molecular mass natural bioactive compounds such as polyphenols (Lee et al. 2006). Despite the advantages of microwave and FIR drying, little data currently exist on the use of these techniques for the dehydration of spices and leafy herbs. Also, to the best of our knowledge, no reports were available on the variations of phenolic composition of sage plants under different drying methods. Therefore, the purpose of the present work was to study the effects of seven drying methods on the antioxidant capacity and contents of antioxidant polyphenolic compounds in S. officinalis aerial parts. This information is needed in order to maximize the quantity and quality of antioxidant phenolics in dried sage plants.
Materials and Methods Chemicals Pure methanol of high-performance liquid chromatography (HPLC)-grade was purchased from Merck (Darmstadt, Germany). Sulfuric acid, acetic acid, and trichloroacetic acid were purchased from Sigma-Aldrich (Steinheim, Germany). Butylated hydroxytoluene (BHT), β-carotene, linoleic acid, ethylenediaminetetraacetic acid, 3-(2-pyridyl)-5,6-bis(4phenyl-sulfonic acid)-1,2,4-triazine (ferrozine), iron(II) chloride (FeCl2), 1,1-diphenyl-2-picrylhydrazyl (DPPH), and polyvinyl polypyrolidone were purchased from Sigma. Folin-Ciocalteu reagent, aluminum chloride, sodium nitrite, and sodium carbonate were purchased from Aldrich. Authentic standards of phenolic compounds were purchased from Fluka (Fluka AG, Buchs, Switzerland) and Riedel-de Haën (Riedel-de Haën AG, Seelze, Germany). Stock solutions of these compounds were prepared in HPLC-grade methanol. All other chemicals used were of analytical grade. Plant Material and Drying Process Aerial parts of sage (S. officinalis L.) were collected in April 2009 from a house garden in the region of Hammam-Chatt in the southern suburbs of Tunis (Tunisia): 36°43′49″ N and 10°22′98″ E, 2 m above sea level (average annual minimum temperature 0 13.2 °C; average annual maximum temperature 023.5 °C; and average annual precipitations 0 38.5 mm). The identity of the plant was confirmed by Prof. Abderrazzak Smaoui, taxonomist, and a voucher specimen was deposited in the herbarium at the Biotechnological Centre of Borj-Cedria under the reference number LN 08002. Plant materials obtained were separated into two groups, one fresh and another to be subjected to various drying conditions. Thirty grams of the fresh plants were used to determine the dry mass after oven drying to constant mass at 105 °C. The other group of plants was used for
Food Bioprocess Technol
drying treatments; for this, fresh samples were divided into seven batches containing three sets of 30 g each. The plant batches were dried by using one of the following methods: (a) air drying at shade and ambient temperature (22 °C); (b) drying in a hot air oven with natural convection at 45 °C; (c) drying in a hot air oven with natural convection at 65 °C; (d) drying in a microwave oven at 600 W/30 g of fresh plant; (e) drying in a microwave oven at 800 W/30 g of fresh plant; (f) drying in an infrared moisture analyzer at 45 °C; and (g) drying in an IR moisture analyzer at 65 °C. The drying conditions employed in each of these methods were selected after conducting trials to achieve a percentage moisture content of
